Forthcoming cellular system standards, such as the so-called “Long-Term Evolution” (LTE) systems developed by participants in the 3rd-Generation Partnership Project (3GPP), will provide a much larger degree of flexibility than currently operating wireless networks. In particular, systems deployed according to Release 10 of the 3GPP LTE specifications will be better able than existing systems to exploit the full potential of the new technologies introduced in LTE, both in terms of system and per-user throughput, and will be better suited for co-existence and deployment in legacy bands.
A mobile station (a user equipment, or UE, in 3GPP terminology) designed for such future standards will generally be required to support a wide range of bandwidths, in many cases aggregated within or over multiple bands. Carrier aggregation, in which two or more separately modulated carrier signals in distinct frequency bands are simultaneously used to carry uplink or downlink traffic for a given mobile station, may be viewed as a scheme for providing flexible bandwidth configuration on a sub-frame basis. With this dynamic re-allocation of potentially large chunks of bandwidth, future systems will be able to quickly respond to users' varying needs for data transmission throughput.
In such a multi-carrier system, such as for an LTE release-10 connection between a network and mobile station, there will be an active set of carriers that are available for carrying traffic for that mobile; these carriers are referred to as component carriers. The mobile station will not be required to continuously receive and transmit on all component carriers in the active set—a given component carrier needs to be processed by the mobile station's receiver or transmitter only if there is a data transmission assignment or grant for that component carrier.
Generally, multiple component carriers need to be simultaneously used for a given mobile station only if those data transmissions are frequent and large enough. As a result, discontinuous-reception (DRX) and discontinuous-transmission (DTX) mechanisms will be used to allow the mobile station to power down parts of the receiver and transmitter during times when no data needs to be received or transmitted on one or more of the component carriers in the active set—this approach allows for a dramatic reduction in power consumption when data throughput requirements are very low or moderate, compared to the power consumed during maximum throughput scenarios, i.e., when all of two or more available component carriers are fully utilized. Indeed, the use of such schemes is generally considered to be a prerequisite to obtain an acceptable level of power consumption in multi-carrier-capable mobile stations.
In the standardization of multi-carrier operation in LTE release 10, the exact operation of DRX and DTX has not yet been specified. In particular, issues regarding whether and how DRX and DTX for one component carrier will relate to DRX and DTX for other component carriers has not been resolved. One possibility is that all component carriers always follow the same DRX/DTX cycle. An alternative approach that provides a greater degree of flexibility is to permit each component carrier to have its own independent DRX/DTX cycle.